The invention discloses a construction technology of slag stacking behind a concrete faced rock-fill dam and relates to the technical field of water and electricity hydraulic engineering. According to the construction technology of the slag stacking behind the concrete faced rock-fill dam, a waste slag area is arranged behind the concrete faced rock-fill dam, waste slags from main dam foundation, shore protection excavation, quarry excavation and temporary project excavation, the top and side slops of the waste slag area are provided with greening and water protection measures, a riding track is arranged at an appropriate elevation, and a drainage edge body, a drainage gallery and a drainage channel which is used for draining seepage water inside the slag stacking body and served as a main dam are arranged inside a slag stacking body behind the dam; a slag yard is arranged behind the dam, the slag stacking body directly presses a downstream dam surface, land acquisition and immigrants at the slag yard and a connecting road are reduced; the waste slag area is close to an engineering excavation area and accordingly waste slag haul distance is reduced; drainage and protection measures of the main dam can be partially utilized and accordingly the slag yard engineering protection amount is reduced; the slag stacking body can be served as dam toe weight and accordingly the dam body stability, particularly the anti-seismic is increased; the structure of the slag yard behind the main dam is economic and environmental friendly and can be widely applied to rock-fill dam construction of the water and electricity hydraulic engineering.